Updated: 3 killed, more than 140 injured in Boston Marathon bombing

April 15, 2013 at 2:01 p.m.Updated April 14, 2013 at 11:15 p.m.

BOSTON (AP) – Two bombs ex ploded in the crowded streets near the finish line of the Boston Marathon on Monday, killing at least three people and in juring more than 140 in a bloody scene of shattered glass and severed limbs that raised alarms that terrorists might have struck again in the U.S.

A White House official speaking on condition of anonymity because the investigation was still unfolding said the attack was being treated as an act of terrorism.

President Barack Obama vowed that those responsible will “feel the full weight of justice.”

As many as two unexploded bombs were also found near the end of the 26.2-mile course as part of what appeared to be a well-coordi nated attack, but they were safely disarmed, according to a senior U.S. intelligence of ficial, who also spoke on con dition of anonymity because of the continuing investiga tion.

The fiery twin blasts took place about 10 seconds and 100 yards apart, knocking spectators and at least one runner off their feet, shatter ing windows and sending dense plumes of smoke rising over the street and through the fluttering national flags lining the route. Blood stained the pavement, and huge shards were missing from window panes as high as three stories.

“They just started bringing people in with no limbs,” said runner Tim Davey of Rich mond, Va. He said he and his wife, Lisa, tried to shield their children’s eyes from the grue some scene inside a medical tent that had been set up to care for fatigued runners, but “they saw a lot.”

“They just kept filling up with more and more casual ties,” Lisa Davey said. “Most everybody was conscious. They were very dazed.”

As the FBI took charge of the investigation, authorities shed no light on a motive or who may have carried out the bombings, and police said they had no suspects in cus tody. Officials in Washington said there was no immediate claim of responsibility.

Police said three people were killed. An 8-year-old boy was among the dead, accord ing to a person who talked to a friend of the family and spoke on condition of anonymity.

Hospitals reported at least 144 people injured, at least 17 of them critically. The vic tims’ injuries included bro ken bones, shrapnel wounds and ruptured eardrums.

At Massachusetts General Hospital, Alisdair Conn, chief of emergency services, said: “This is something I’ve never seen in my 25 years here ... this amount of carnage in the civilian population. This is what we expect from war.”

Some 23,000 runners took part in the race, one of the world’s oldest and most pres tigious marathons.

One of Boston’s biggest an nual events, the race winds up near Copley Square, not far from the landmark Pruden tial Center and the Boston Public Library. It is held on Patriots Day, which commem orates the first battles of the American Revolution at Con cord and Lexington in 1775.

Boston Police Commission er Edward Davis asked peo ple to stay indoors or go back to their hotel rooms and avoid crowds as bomb squads methodically checked parcels and bags left along the race route. He said inves tigators didn’t know whether the bombs were hidden in mailboxes or trash cans.

He said authorities had re ceived “no specific intelli gence that anything was go ing to happen” at the race.

The Federal Aviation Administration barred low-flying aircraft within 3.5 miles of the site.

“We still don’t know who did this or why,” Obama said at the White House, adding, “Make no mistake: We will get to the bottom of this.”

With scant official informa tion to guide them, members of Congress said there was little or no doubt it was an act of terrorism.

“We just don’t know whether it’s foreign or do mestic,” said Rep. Michael McCaul, R-Texas, chairman of the House Committee on Homeland Security.

A few miles away from the finish line and around the same time, a fire broke out at the John F. Kennedy Library. The police commissioner said that it may have been caused by an incendiary device but that it was not clear whether it was related to the bombings.

The first explosion oc curred on the north side of Boylston Street, just before the finish line, and some peo ple initially thought it was a celebratory cannon blast.

When the second bomb went off, spectators’ cheers turned to screams. As sirens blared, emergency workers and National Guardsmen who had been assigned to the race for crowd control began climbing over and tearing down temporary fences to get to the blast site.

The bombings occurred about four hours into the race and two hours after the men’s winner crossed the finish line. By that point, more than 17,000 of the athletes had finished the marathon, but thousands more were still running.

The attack may have been timed for maximum carnage: The four-hour mark is typically a crowded time near the finish line because of the slow-but-steady recreational runners completing the race and because of all the friends and relatives clustered around to cheer them on.